1. Field
The embodiments of the present invention encompass a new fullerene derivative that is useful as an organic semiconductor material. The embodiments of the present invention also encompass an organic semiconductor device, particularly a field-effect transistor (hereinafter referred to as “FET”), using the fullerene derivative, and a method of producing the FET.
2. Related Art
Heretofore, it has been shown that fullerene, a soccer-ball-shaped carbon allotrope (hereinafter referred to as “C60”), exhibits distinguished n-type semiconductor characteristics among organic semiconductor materials, and a fullerene film formed by an ultrahigh vacuum process, such as molecular beam epitaxy, achieves an electron mobility equivalent to that of amorphous silicon. For example, see S. Kobayashi et al., “Fabrication and characterization of C60 thin-film transistors with high field-effect mobility”, Applied Physics Letters, Vol. 82, No. 25, pp 4581-4583, (2003). In practice, it is difficult for such conventional film-forming techniques to increase the film-forming area and are more costly to produce. Thus, there is a need for developing a film-forming technique based on a coating process capable of contributing to increasing the film-forming area and reducing production cost.
The technique of producing an organic FET by a spin coating process using [6,6]-phenyl C61-butyric acid methyl ester (PCBM), a C60 derivative, is also known. For example, see Christoph Waldauf et al., “Solution-Processed Organic n-Type Thin-Film Transistors”, Advanced Materials, Vol. 15, No. 24, pp 2084-2088 (2003).
The technique is also known of incorporating an alkyl chain to C60 to prepare C60-fused N-methylpyrrolidine-meta-C12 phenyl (C60MC12) as another C60 derivative so as to enhance crystallinity of a thin film to be formed, wherein C60MC12 exhibits a higher electron mobility (0.067 cm2/Vs) than that of PCBM. For example, see Japanese Patent Laid-Open Publication No. 2006-60169 (JP 2006-60169A); M. Chikamatsu et al., “Solution-processed n-type organic thin-film transistors with high field-effect mobility”, Applied Physics Letters, Vol. 87, p 203504, (2005).